SIP trunking

You already have phone numbers on a licensed Indian carrier — an Airtel or Tata enterprise trunk, an Exotel or Vobiz account, or a PBX that fronts one of those. This page is how you point that trunk at Tone so a Tone agent answers your inbound calls and places your outbound ones, without moving a single number.

What Tone is, and is not, on a trunk

Tone is an application platform: in regulatory terms, a cloud EPABX. Your carrier stays the licensed operator that interconnects with the phone network; Tone never terminates a call onto the PSTN itself. Every packet of audio stays in Mumbai (ap-south-1). Every outbound dial still passes the pre-dial compliance gate, and every call is recorded in your call log with the same webhooks, transcripts and recordings a Tone-number call gets.

What you keep: your numbers, your carrier contract, your rates. What Tone runs: the agent, the compliance gate, recording, billing.

Connection details

Two ways your trunk can identify itself

• IP allowlist — you tell Tone the public IPv4 ranges your carrier or PBX sends from. This is how Exotel vSIP and most enterprise SBCs work. /24 or narrower; private ranges are refused.
• Digest credentials — Tone issues a username and a password, shown once when the trunk is created (or rotated). Use this when your side has no fixed address, or in addition to the allowlist.

For outbound calls Tone dials your carrier. You give Tone the host, port and transport your carrier publishes for termination, and either allowlist Tone's IPs at the carrier or give Tone a username and password to present.

Create a trunk

Trunks are an organization-level resource and need a verified (KYC) organization and the SIP trunking capability enabled by Tone support.

POST /v1/sip-trunks
{
  "name": "Airtel HQ trunk",
  "inboundAuth": "ip_acl",
  "ipAcl": ["203.0.113.0/28"],
  "outboundHost": "sbc.example.com",
  "outboundPort": 5061,
  "outboundTransport": "tls",
  "outboundAuthUsername": "tone",
  "outboundAuthPassword": "…",
  "outboundNumberFormat": "e164",
  "maxConcurrent": 20
}

The response carries the trunk and, once, the connection block your carrier console needs — including the digest password if you chose credentials:

{
  "trunk": { "id": "…", "status": "pending_verification", "…": "…" },
  "connection": {
    "host": "sip.usetone.ai", "port": 5061, "transport": "tls",
    "ips": ["…"], "realm": "sip.usetone.ai",
    "username": "t_9f2c…", "password": "…"
  }
}

A new trunk is pending_verification until Tone staff approve it; approval is usually same-day. Rotate credentials with POST /v1/sip-trunks/{id}/credentials/rotate (the old ones stop working immediately). POST /v1/sip-trunks/{id}/test sends a SIP OPTIONS ping to your outbound host and reports reachability and round-trip time.

Add your numbers

Each number your carrier will send to Tone becomes an ordinary Tone phone number — with an agent, recording switch and call log — but with no rental, because you already pay your carrier for it.

POST /v1/sip-trunks/{id}/numbers
{ "e164": "+918044001234", "agentId": "…" }

Inbound calls to the number are answered only when they arrive on that trunk. A call for your number arriving from another trunk is refused, which is what stops one tenant's misconfiguration from reaching another's agent.

Outbound calls and campaigns

Nothing changes on the API: POST /v1/calls with a trunk number as numberId, or a campaign using it, dials through your carrier with the number as caller ID. The compliance gate (calling window, your DNC list, consent) runs before every dial exactly as it does for Tone numbers. Busy, no-answer and failed outcomes reach your webhooks with the same dispositions.

Your carrier decides which caller IDs it accepts; Tone presents the trunk number in From and P-Asserted-Identity. Some Indian carriers want the destination in national format with a leading zero rather than +91: set outboundNumberFormat to national0 if your first test call is rejected with a number-format error.

Billing

A call on your own trunk bills the agent + platform components — ₹5.50 per minute list — and no telephony component, because the carrier minute is yours. If the number is also routed to your own voice stack (byo_ws), only the platform component applies. There is no monthly rental on trunk numbers.

Refusals you may see

Each refusal is also visible on the trunk's page in the dashboard with the reason spelled out.

Carrier guides

• Exotel vSIP — PoPs and transports, the X-Exotel-AccountSid header you must send, and the Exophone rule that rejects outbound calls.
• Vobiz — digest or IP identity, and the number format that usually needs changing.
• Tata Smartflo — what to put on the provisioning form, since Tata configures the trunk rather than you.
• Airtel (via your SBC) — front the trunk with your own SBC and route selected DIDs to an agent.
• Asterisk and FreePBX — PJSIP config, the FreePBX fields that generate it, and the three settings that are load-bearing.

Any standards-compliant SIP trunk that can send INVITE to a hostname over TLS, and accept INVITE from a fixed IP, works with the details above — these pages just save you the round trips.

Tone numbers to your hosted platform

If instead you want a Tone +91 number delivered to Retell, Vapi, ElevenLabs or LiveKit over SIP, that is the per-number trunk described in Tone Media Streams.